Irinotecan (CPT-11) is a semisynthetic derivative of camptothecin which acts by inhibiting topoisomerase I. It is our hypothesis that orally administered irinotecan HC1 (CPT-11) is a potent and effective antitumor agent. We are undertaking a phase I trial of oral irinotecan HC1 (CPT-11) in patients with advanced solid tumors. The objectives of the trial are: 1) to determine the MTD and the DLT of CPT-11 when administered orally once per day for five consecutive days every three weeks, 2) to define the safety profile of CPT-11 when administered orally on this schedule, 3) to characterize the single- and multiple-dose pharmacokinetics of CPT-11 and its metabolites, SN-38 and SN-38 glucuronide (SN-38G), and 4) to detect any evidence of antitumor activity.